Realization of low specific-contact-resistance on N-polar GaN surfaces using heavily-Ge-doped n-type GaN films deposited by low-temperature reactive sputtering technique

Abstract

We developed a low-temperature ohmic contact formation process for N-polar GaN surfaces. Specific-contact-resistances of 9.4 × 10−5 and 2.0 × 10−5 Ω·cm2 were obtained using Ti/Al metal stacks on heavily-germanium-doped GaN films, which were deposited at 500 °C and 600 °C using a radical-assisted reactive sputtering method, respectively. The electrode sintering temperature was as low as 475 °C. Carrier concentrations for the 500 °C and 600 °C samples were 2.6 × 1020 and 1.8 × 1020 cm−3, respectively. These results suggest that this method is highly effective in reducing the contact resistance of GaN devices with low thermal budgets.

III-Nitride Materials: Properties, Growth, and Applications

“…Benefiting from the inversed polarization field, N-polar GaN may surmount the bottlenecks faced by their incumbent Ga-polar counterparts [60,61]. Achievements have been made in the metal-organic chemical vapor deposition (MOCVD) growth of N-polar GaN [62][63][64][65][66]. Additionally, HEMTs based on N-polar GaN have exhibited transcendental performance in some aspects [67][68][69].…”